Well, it's getting to be the time for robber screens again. The heavy flows are over here and the bees are looking to add weak hives stores to their own.
One thing I learned this year is to have a 3/8" square hole near one edge like the queen breeders do. The hive can still defend the hive, have good ventilation, but if a virgin queen goes out, she can find her way back in. Every hive that I had robber screens on this spring went queenless! Here is some design suggestions plus some addition information:
http://nordykebeefarm.com/forum/forum_topics.asp?FID=6
I don't use robber screens. I find that putting a slatted rack between the brood box and the bottom board acts as a good guard station, the excess bees hangout there and act as extra guards.
Hi Brian,
I use both. I have the original Killion design and a shorter custom design I made to fit my older bottom boards for ventilation. I still find the robber screens effective and after becoming used to it, the robber screen doesn't affect hive life.
I have a video of a robber bee trying to get in. She runs all over the screen, never quite making the top of the screen. I have seen another go up the side and over the top so it's not 100% effective at keeping individuals out. Where it really shines is where large a number of bees start robbing. An ounce of prevention is worth a pound of cure.
Using a robber screen give me peace of mind that I don't have to worry about weaker hives having to be defensive. It allows me to make inspections without defensive behaviour from the bees.
The original article from Bee Culture that I posted (with permission) with the information on the web site http://nordykebeefarm.com/forum/forum_topics.asp?FID=6 does a better job of explaining so I won't duplicate it here.